1. Field of Invention
This invention relates to the use of wave springs to cushion a shoe. Wave springs allow for reduced impact on the user during foot strike, thus increasing comfort and decreasing injury. Also, the wave springs will return a portion of the impact energy to the user for more efficient jumping, walking and/or running.
2. Description of the Related Art
People involved in normal exercise programs are always seeking new equipment that can minimize the risk of injury to parts of the body caused by stress due to a foot strike. Athletes are also continually looking for ways to improve their performance levels in a variety of athletic and aerobic events that involve walking, running, or jumping while, at the same time, taking steps to reduce the wear and tear attendant to the pounding endured by joints and bones. This can be achieved to some degree by the use of improved sporting equipment and more specifically improved shoes for both athletes and non-athletes.
When participating in sports, especially high impact sports such as volleyball and basketball, the foot of the participant, specifically the ball and heel areas, are prone to extreme mechanical stress due to the force that will be imparted when the foot strikes a relatively incompressible surface. This force, which will vary depending on the type of activity that a person is involved in and the mass of the person, can be as large as five times the body weight of the participant. The reaction force resulting from contact with a non-yielding surface causes great shock to the body that can injure the lower back and all rotating joints of the leg.
Unlike events that involve jumping, the mechanics of running or walking involve a prescribed set of motions insofar as the foot is concerned. Except in those events that involve sprinting, the heel impacts the ground first, the weight then shifts forward onto the ball of the foot in a rolling manner with the toe region providing the last contact with the ground. The initial impact in the heel area is of special interest with non-sprinting runners because it is here that landing forces come into play. It is desirable to absorb as much impact energy as possible, consistent with providing a stable landing and without slowing down the runner. It is also desirable to avoid the complete loss of energy absorbed by the shoe at impact. Also, since the ball and toe areas of the foot are the last to leave the surface in contact with the ground, it is desirable to recover some of the landing energy absorbed in the initial impact. A number of patents related to shoe constructions, which are variously designed to address one or more of the desirable shoe features discussed above, are reviewed below.
U.S. Pat. No. 5,896,679 discloses an article of footwear with a spring mechanism located in the heel area of a shoe, including two plates connected one to the other, and attachment to the lower surface of the shoe sole. The invention of the '679 patent provides a heel mechanism that absorbs the shock or impact foot strikes. U.S. Pat. No. 5,743,028 (T. D. Lombardino) discloses a plurality of vertically oriented compression springs located in the heel area of a running shoe. The springs of the '028 patent are housed in a hermetically sealed unit filled with a pressurized gas that, in combination with the springs, provides a shock absorbing and energy return system. The springs have a substantially coiled appearance in which each spiral coil must provide a torsional spring force and collapse in a vertical stack commonly called the solid height when totally compressed. Because of their design, these springs must have significant free heights to accommodate large deflections. U.S. Pat. No. 4,815,221 (Diaz) discloses an energy control system including a spring plate having a plurality of spring projections distributed over the surface of the plate, which is placed in a vacuity formed within the mid-sole of an athletic shoe. U.S. Pat. No. 5,511,324 (R. Smith) discloses a shoe in which a coil spring extends through a hole in the heel area of the wedge sole of an athletic shoe. U.S. Pat. No. 5,437,110 (Goldston, et al.) discloses an adjustable shoe heel spring and stabilizer device for a running shoe, including a spring mechanism disposed in the mid-sole of the shoe. The shoe heel spring includes a cantilevered spring member and an adjustable fulcrum. A shoe designed specifically for jumping is disclosed in U.S. Pat. No. 5,916,071 (Y. Y. Lee). Lee discloses a shoe mounted on a frame containing a coil spring that extends horizontally from the regions of the frame located at the toe and heel areas of the shoe. The coil spring expands and contracts during walking and jumping. U.S. Pat. No. 4,492,046 (Kosova) discloses a running shoe that includes a spring wire located in a longitudinal slot in the shoe sole, extending from the back edge thereof into the arch region. U.S. Pat. No. 2,447,603 (Snyder) discloses a U-shaped spring plate disposed between the heel of the shoe and a rear portion of the shoe sole. Several other U.S. patents of related art are: U.S. Pat. No. 5,875,567 (R. Bayley); U.S. Pat. No. 5,269,081 (Gray); U.S. Pat. No. 2,444,865 (Warrington); U.S. Pat. No. 3,822,490 (Murawski); U.S. Pat. No. 4,592,153 (Jacinta); and, U.S. Pat. No. 5,343,636 (Sabol); U.S. Pat. No. 5,435,079 (Gallegos); U.S. Pat. No. 5,502,901 (Brown); U.S. Pat. No. 5,517,769 (Zhao); and U.S. Pat. No. 5,544,431 (Dixon).
Revisiting and expanding the above mentioned desirable attributes of a shoe of this type, there is a need for a shoe that enhances the performance of the wearer by providing a substantial spring force working through a significant distance while requiring a minimum volume for deployment. In addition there is a need for a shoe design that also assists in propelling the foot off the ground while still maintaining sufficient lateral stability of the shoe for quick side-to-side movement of the wearer. This performance enhancement can be achieved by temporarily storing the shock energy imparted by foot strike and returning a substantial amount of the energy to the wearer's foot during the propelling-off portion of the stride. Also, there is a need to assure adequate spring fatigue life by limiting maximum stresses and preventing compression to the spring's solid height.
The prior art cited above has disclosed spring devices in athletic shoes for the purposes of absorbing shock and returning energy to the wearer's foot.
As can be seen from the background art, there have been many attempts to add spring cushioning to shoes. However, one only need to look at the current market to see that spring cushioned shoes are not commonly available.